Polymer simulations guide the detection and quantification of chromatin loop extrusion by imaging

Area of Science:

• Genomics and Molecular Biology
• Cellular and Structural Biology

Background:

• Genome-wide chromosome conformation capture (Hi-C) identified topologically associating domains (TADs) and loops, crucial for genome regulation.
• Chromatin loops and TADs are hypothesized to form via DNA extrusion mediated by the cohesin complex.
• Direct visualization and quantification of DNA loop extrusion in single cells remain significant challenges.

Purpose of the Study:

• To investigate the feasibility of detecting and quantitatively characterizing DNA loop extrusion using imaging techniques.
• To explore conditions under which DNA loop extrusion can be visualized and measured in fixed and live cells.
• To establish analytical methods for quantifying loop formation frequency, loop lifetime, and extrusion speed.

Main Methods:

• Utilized polymer simulations to model DNA extrusion processes.
• Developed dedicated analysis methods for imaging data.
• Simulated imaging of fluorescently labeled loci near loop or TAD anchors in fixed and live cells.

Main Results:

• Demonstrated that DNA loop extrusion can be detected and quantified from fixed cell images under realistic conditions.
• Showed that loop formation frequency can be quantified using fixed-cell imaging alone.
• Established that loop lifetime and extrusion speed can be estimated from dynamic live-cell imaging data.

Conclusions:

• The study provides a framework for the quantitative characterization of DNA loop extrusion in cellular contexts.
• Proposed imaging conditions and analytical methods enable systematic study of loop extrusion dynamics.
• This work lays the foundation for understanding the role of loop extrusion in genome organization and function.